Air filters are widely used on internal combustion engines driving heavy equipment, combines, trucks and the like to remove impurities from the air before the air enters the engine for combustion. Such air filters typically trap and remove from the air large quantities of impurities such as dust, dirt, sand, and even rocks. After a period of use, the filters become clogged with trapped impurities which must be removed in order for the filters to be useful once again.
Various approaches have been utilized to clean air filters, with the approaches generally using forced air flow through the filters. The forced air flow may be created by using either air pressure, air suction, or a combination of both. One problem encountered with conventional air cleaning apparatuses has been that the air flow provided through the filter may not be the particular air flow best suited for cleaning that particular filter. For example, a common annular air filter used on larger engines driving trucks, heavy equipment and the like which traps impurities as they move from the filter's outer periphery toward its center may best be cleaned by an air flow in an outward direction, away from the center of the filter, thereby driving the trapped particles back along the path by which they entered the filter. Such air flow may be created by an outward air suction applied to the outer periphery of the filter, by an outward air pressure from the inner periphery of the filter, or by a combination of such suction and pressure. However, most well known filter cleaning apparatuses are capable of producing air flow in only one direction relative to the filter. Examples of such conventional filter cleaners may be seen in U.S. Pat. No. 3,360,907 (pressurized air applied to outer periphery); U.S. Pat. No. 3,345,805 (suction applied to outer periphery); U.S. Pat. No. 4,364,755 (suction applied to inner periphery); and U.S. Pat. No. 4,266,953 (pressure applied to one side and suction to the other).
In cleaning an air filter, it is also desirable to vibrate the filter in order to shake loose trapped impurities. In one known arrangement, this vibration is transferred to the filter by striking the filter directly. A problem associated with this approach is that it tends to create wear and tear of both the striking mechanism and the filters being cleaned. Examples of such striking arrangements are provided in U.S. Pat. No. 4,345,353 and U.S. Pat. No. 4,258,451. Alternatively, the supporting structure for the filter may be shaken, thereby causing the filter itself to shake, as illustrated in U.S. Pat. Nos. 4,328,014 and 3,639,940.
When cleaning an air filter using forced air flow, it is also desirable that the air flow be applied to the entire peripheral surface area of the filter, in order to assure that the filter is thoroughly cleaned. This has typically been accomplished by rotating the filter to expose its entire circumference to air flow, and by moving the source of the air flow back and forth along the depth of the filter's periphery to fully expose that dimension of the filter to air flow. Examples of these approaches are provided in U.S. Pat. Nos. 3,360,907 and 3,345,805.